It is desirable that portable information processing devices such as tablet devices and smart phones operate with effective use of limited power. Reduction in power consumption of information processing devices is therefore a major issue.
Power consumption of an information processing device can be reduced by stopping a high-frequency oscillator that is a clock source in processing tasks by a processor when the processor is in a standby state (a state in which the processor continues waiting for an interrupt) waiting for an input from a device. Power consumption of an information processing device can further be reduced by stopping power supply to a memory from/to which data are read/written by a processor in the standby state.
When the processor receives an interrupt and the information processing device resumes from the standby state, however, there is a problem that it takes time for the processor to be ready for reading/writing data from/to the memory if the high-frequency oscillator is first started and the memory is then initialized after the clock has become stable.